Conductive polymer materials are increasingly replacing metal materials for electromagnetic interference (EMI) shielding, radio frequency interference (RFI) shielding and electrostatic discharge ESD protection. Typically, metal shields increase part counts, require extra manufacturing steps to assembly, and add weight to the finished product. Using conductive polymers for EMI, RFI, and EDS shielding provides weight reduction, reduced manufacturing steps (and thus cost), and a greater freedom of design.
As shown in FIG. 1, the conductive polymers 1 have a conductive filler material 2, e.g. metal fibers, embedded in a nonconductive polymer matrix 3. These conductive polymers provide good through-plane electrical conductivity, but have a high surface resistance. For shielding applications, there needs to be transfer of charge from the inner conductive filler material to a ground connected to the surface of the conductive polymer material, which the high surface resistance prohibits. There are ways to create low resistance paths to the surface of conductive polymers but it adds complexity and therefore cost to the manufacturing process.
Additionally, the conducting efficiency of conductive polymers is low due to the low percentage of interconnections between the conductive filler particles. Given the amount of metal incorporated, the resistance value is many times higher than the amount of metal actually inside. Improving the interconnection of the metal fillers will decrease resistance and improve shielding properties of the composite. Improving this interconnection between filler will also reduce the percolation threshold, or how much filler is required to achieve adequate conductivity.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.